Nitrous oxide as diazo transfer reagent

Abstract

Nitrous oxide, commonly known as "laughing gas", is formed as a by-product in several industrial processes. It is also readily available by thermal decomposition of ammonium nitrate. Traditionally, the chemical valorization of N₂O is achieved via oxidation chemistry, where N₂O acts as a selective oxygen atom transfer reagent. Recent results have shown that N₂O can also function as an efficient diazo transfer reagent. Synthetically useful methods for synthesizing triazenes, N-heterocycles, and azo- or diazo compounds were developed. This review article summarizes significant advancements in this emerging field.

Scheme 1. Nitrous oxide is formed as a side product during the industrial production of nitric acid (a) and adipic acid (b).

Scheme 2. Synthesis of nitrous oxide by thermal decomposition of ammonium nitrate (a) or by catalytic oxidation of ammonia (b).

Scheme 3. The use of nitrous oxide as an O-atom donor: synthesis of phenol by catalytic oxidation of benzene (a), and synthesis of cyclododecanone by non-catalytic oxidation of 1,5,9-cyclododecatriene, followed by hydrogenation (b).

Scheme 4. Upon chemical activation, nitrous oxide typically acts as O-atom donor. This review focuses on reactions in which N₂O functions as diazo transfer reagent.

Scheme 5. Cooperative covalent capture of N₂O by (semi-)metal complexes (Dipp = 2,6-C₆H₃iPr₂).

Scheme 6. Covalent capture of nitrous oxide by frustrated Lewis pairs (FLPs).

Scheme 7. Covalent capture of N₂O by N-heterocyclic carbenes (NHCs).

Scheme 8. Covalent capture of N₂O by mixtures of N-heterocyclic carbenes and B(C₆F₅)₃.

Scheme 9. Covalent capture of N₂O by lithium amides.

Scheme 10. Synthesis of aryl azides.

Scheme 11. Synthesis of triazenes by reactions of N₂O-derived aminodiazotates with Grignard reagents.

Scheme 12. Alkynyl triazenes as versatile starting materials in synthetic organic chemistry.

Scheme 13. Synthesis of a terminal alkynyl triazene and its functionalization.

Scheme 14. Synthesis of pyrazoles.

Scheme 15. Syntheses of benzotriazines.

Scheme 16. Synthesis of benzo[c]cinnoline.

Scheme 17. Syntheses of triazolopyridines.

Scheme 18. Synthesis of azobenzene and azo-bridged ferrocene.

Scheme 19. Synthesis of cationic azo dyes from NHC–N₂O adducts.

Scheme 20. Synthesis of azo-bridged N-heterocyclic olefins.

Scheme 21. Synthesis of diazomethane (a and b) and addition of N₂O to a cyclic alkyne (c).

Scheme 22. Synthesis of diazo compound 53.

Scheme 23. Synthesis of N-heterocyclic diazoolefins.

Scheme 24. The multifaceted chemistry of N-heterocyclic diazoolefins.

Scheme 25. The reaction of a dimethylated N-heterocyclic olefin with nitrous oxide.

Scheme 26. Synthesis of the diazophosphorus ylide 61.

Alexandre Genoux

Kay Severin